U.S. patent number 8,044,548 [Application Number 12/438,216] was granted by the patent office on 2011-10-25 for permanent-magnet-type rotating electrical machine.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Masanori Arata, Kazuto Sakai.
United States Patent |
8,044,548 |
Sakai , et al. |
October 25, 2011 |
Permanent-magnet-type rotating electrical machine
Abstract
An object of the present invention is to provide a
permanent-magnet-type rotating electrical machine capable of
realizing a variable-speed operation at high output in a wide range
from low speed to high speed and improving efficiency and
reliability. The permanent-magnet-type rotating electrical machine
of the present invention includes a stator provided with a coil and
a rotor in which there are arranged a low-coercive-force permanent
magnet whose coercive force is of such a level that a magnetic
field created by a current of the stator coil may irreversibly
change the flux density of the magnet and a high-coercive-force
permanent magnet whose coercive force is equal to or larger than
twice that of the low-coercive-force permanent magnet. At the time
of high-speed rotation with a voltage of the permanent-magnet-type
rotating electrical machine being around or over a power source
maximum voltage, the low-coercive-force permanent magnet is
magnetized with a magnetic field created by a current in such a way
as to decrease total linkage flux of the low- and
high-coercive-force permanent magnets, thereby adjusting a total
linkage flux amount.
Inventors: |
Sakai; Kazuto (Yokosuka,
JP), Arata; Masanori (Yokohama, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Tokyo, JP)
|
Family
ID: |
39106507 |
Appl.
No.: |
12/438,216 |
Filed: |
August 23, 2006 |
PCT
Filed: |
August 23, 2006 |
PCT No.: |
PCT/JP2006/316510 |
371(c)(1),(2),(4) Date: |
February 20, 2009 |
PCT
Pub. No.: |
WO2008/023413 |
PCT
Pub. Date: |
February 28, 2008 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20090236923 A1 |
Sep 24, 2009 |
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Current U.S.
Class: |
310/156.43;
310/156.53; 310/156.56; 310/156.36 |
Current CPC
Class: |
H02K
21/16 (20130101); H02K 1/2766 (20130101); H02K
29/03 (20130101) |
Current International
Class: |
H02K
21/12 (20060101) |
Field of
Search: |
;310/156.43,154,156,153.36,156.53,156.56 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1516915 |
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Jul 2004 |
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CN |
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6-189481 |
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Jul 1994 |
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JP |
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7-336919 |
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Dec 1995 |
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JP |
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8-009610 |
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Jan 1996 |
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JP |
|
11-027913 |
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Jan 1999 |
|
JP |
|
11-136912 |
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May 1999 |
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JP |
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2002-044889 |
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Feb 2002 |
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JP |
|
2002-136011 |
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May 2002 |
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JP |
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WO 03/079516 |
|
Sep 2003 |
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WO |
|
Other References
Nasar et al, "Permanent Magnet, Reluctance and Self Synchronous
Motors", CRC Press, 1993, pp. 37-39. cited by examiner .
Chapman, "Electric Machinery Foundation", McGraw Hill, 1991, p.
340. cited by examiner .
wikipedia, p. 7, "Demagnetizing ferromagnets". cited by examiner
.
wikipedia, "Demagnetizing ferromagnets" in p. 7 "Magnet", Feb. 24,
2011. cited by examiner .
Y. Takeda et al., "Design and Control of Interior Permanent Magnet
Synchronous Motor," Interior Permanent Magnet Syncronous Motor,
Oct. 25, 2001, pp. 1-6, English translation 1-12. cited by
other.
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Primary Examiner: Leung; Quyen
Assistant Examiner: Kim; John K
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
The invention claimed is:
1. A permanent-magnet-type rotating electrical machine comprising:
a stator provided with a stator coil; and a rotor having a rotor
core in which there are arranged a plurality of low-coercive-force
permanent magnets and a plurality of high-coercive-force permanent
magnets each coercive force is equal to or larger than twice that
of each low-coercive-force permanent magnet, wherein each
low-coercive-force permanent magnet is arranged in a radial
direction of the rotor that agrees with a q-axis serving as an
inter-polar center axis and is magnetized in a direction orthogonal
to the radial direction, each high-coercive-force permanent magnet
is arranged on the inner circumferential side of the rotor between
two low-coercive-force permanent magnets to be oriented in a
circumferential direction of the rotor and is magnetized in a
direction orthogonal to the circumferential direction of the rotor,
a diametrical section of the rotor is shaped so that the low- and
high-coercive-force permanent magnets surround a part of the rotor
core serving as a magnetic pole portion, and a flux density or both
a flux density and a magnetizing direction of each
low-coercive-force permanent magnet is irreversibly adjusted by
passing a pulse current to the stator coil for a short time, an
amount of the pulse current being adequate to form a magnetic field
that is sufficient to irreversibly change the flux density or both
the flux density and the magnetizing direction of each
low-coercive-force permanent magnet while no magnetization that may
cause irreversible demagnetization occurs on each
high-coercive-force permanent magnet.
2. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the high-coercive-force permanent magnet
is arranged on the outer circumferential side of the rotor core and
the low-coercive-force permanent magnet is arranged on the inner
circumferential side of the rotor core.
3. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein a counter electromotive voltage of the
high-coercive-force permanent magnet generated when the rotor
reaches a maximum rotation speed is set to be equal to or lower
than a withstand voltage of electronic parts of an inverter serving
as a power source of the permanent-magnet-type rotating electrical
machine.
4. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein a flux amount of the high-coercive-force
permanent magnet in a state in which a flux amount of the low- and
high-coercive-force permanent magnets is maximum is smaller than a
maximum flux amount of the low-coercive-force permanent magnet.
5. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the rotor core is shaped so that magnetic
resistance in the direction of the d-axis serving as the polar
center axis of the rotor is small and magnetic resistance in the
direction of the q-axis serving as the inter-polar center axis is
large.
6. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the low-coercive-force permanent magnet
is arranged on the outer circumferential side of the rotor core and
is oriented in the diametrical direction of the rotor and an air
gap side of the rotor core is recessed around a radial outer end of
the low-coercive-force permanent magnet except the radial outer end
part.
7. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the low-coercive-force permanent magnet
is arranged on the outer circumferential side of the rotor core and
is oriented in the diametrical direction of the rotor, a polar
middle part of the rotor core defines an outermost circumferential
part of the rotor core, and an air gap side of the rotor core is
recessed from the polar middle part toward the radial outer end of
the low-coercive-force permanent magnet.
8. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the high-coercive-force permanent magnet
is arranged on the outer circumferential side of the rotor core and
is oriented in the diametrical direction of the rotor and an air
gap side of the rotor core is recessed around a radial outer end of
the high-coercive-force permanent magnet except the radial outer
end part.
9. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the high-coercive-force permanent magnet
is arranged on the outer circumferential side of the rotor core and
is oriented in the diametrical direction of the rotor, a polar
middle part of the rotor core defines an outermost circumferential
part of the rotor core, and an air gap side of the rotor core is
recessed from the polar middle part toward the radial outer end of
the high-coercive-force permanent magnet.
10. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the polar middle part of the rotor core
is composed of a circular arc defined with a maximum radius of the
rotor and a central angle of the circular art of the polar middle
part is in the range of 90 to 140 degrees in electrical angle.
11. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the low-coercive-force permanent magnet
is arranged on the outer circumferential side of the rotor core and
an air-gap-side end of the low-coercive-force permanent magnet is
provided with a magnetic barrier whose circumferential length is
longer than the thickness of the low-coercive-force permanent
magnet.
12. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the magnetic pole portion of the rotor
core is provided with a slit to increase magnetic resistance in the
direction of the q-axis serving as the inter-polar center axis of
the rotor.
13. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein, at the time of high-speed rotation with
a voltage of the permanent-magnet-type rotating electrical machine
being around or over a power source maximum voltage, the
low-coercive-force permanent magnet is irreversibly magnetized with
a magnetic field created by the pulse current of the stator coil in
such a way as to decrease linkage flux of the low- and
high-coercive-force permanent magnets, thereby adjusting a total
linkage flux amount.
14. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein, at the time of low-speed rotation with a
voltage of the permanent-magnet-type rotating electrical machine
being equal to or lower than a power source maximum voltage, the
low-coercive-force permanent magnet is irreversibly magnetized with
a magnetic field created by the pulse current of the stator coil in
such a way as to increase linkage flux of the low- and
high-coercive-force permanent magnets, and at the time of
high-speed rotation with a voltage of the permanent-magnet-type
rotating electrical machine being around or over the power source
maximum voltage, the low-coercive-force permanent magnet is
irreversibly magnetized with a magnetic field created by the pulse
current of the stator coil in such a way as to decrease linkage
flux of the low- and high-coercive-force permanent magnets, thereby
adjusting a total linkage flux amount.
15. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein a flux amount of the low-coercive-force
permanent magnet is irreversibly adjusted with a magnetic field
created by the pulse current of the stator coil in such a way as to
zero a linkage flux amount of the low- and high-coercive-force
permanent magnets.
16. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein a flux amount provided by the
low-coercive-force permanent magnet is equal to a flux amount
provided by the high-coercive-force permanent magnet.
17. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the magnetizing direction of the
low-coercive-force permanent magnet is irreversibly reversed from
one to another according to a magnetic field created by the pulse
current of the stator coil.
18. The permanent-magnet-type rotating electrical machine as set
forth in claim 1, wherein the rotor core is provided with a slit to
reduce demagnetizing fields of the low- and high-coercive-force
permanent magnets acting on each other.
Description
TECHNICAL FIELD
The present invention relates to a permanent-magnet-type rotating
electrical machine.
BACKGROUND TECHNOLOGY
Generally, permanent-magnet motors are classified into two types.
One is a surface-magnet-type motor having permanent magnets adhered
to an outer circumference of a rotor core and the other is an
internal-magnet-type motor having permanent magnets embedded in a
rotor core. For a variable-speed drive motor, the
internal-magnet-type motor is appropriate.
With reference to FIG. 19, a structure of a rotor of the
internal-magnet-type motor will be explained. In FIG. 19, 11 is the
rotor, 12 is a rotor core, and 14 is a high-coercive-force
permanent magnet. An outer circumferential area of the rotor core
12 is provided with rectangular hollows at regular pitches, the
number of the hollows being equal to the number of magnetic poles.
The rotor 11 illustrated in FIG. 19 has four poles, and therefore,
four hollows are formed and the permanent magnets 14 are inserted
therein, respectively. The permanent magnet 14 is magnetized in a
radial direction of the rotor, i.e., in a direction orthogonal to a
side of the rectangular section of the permanent magnet 14 that
faces an air gap. The permanent magnet 14 is usually an NdFeB
permanent magnet having a high coercive force so that it is not
demagnetized with a load current. The rotor core 12 is formed by
laminating electromagnetic sheets through which the hollows are
punched. A related art of this kind is described in "Design and
Control of Internal Magnet Synchronous Motor," Takeda Yoji, et al.,
published by Ohm-sha. A modification of the internal type is
described in Japanese Unexamined Patent Application Publication No.
H07-336919. High-output motors with excellent variable speed
performance are permanent-magnet-type reluctance rotating
electrical machines described in Japanese Unexamined Patent
Application Publication No. H11-27913 and Japanese Unexamined
Patent Application Publication No. H11-136912.
A permanent-magnet-type rotating electrical machine always
generates constant linkage flux from permanent magnets, to increase
a voltage induced by the permanent magnets in proportion to
rotation speed. When carrying out a variable-speed operation from
low speed to high speed, the permanent magnets induce a very high
voltage at high rotation speed. The voltage induced by the
permanent magnets is applied to electronic parts of an inverter,
and if the applied voltage exceeds a withstand voltage of the
electronic parts, the parts will cause insulation breakage. It is
necessary, therefore, to design the machine so that the flux amount
of the permanent magnets is below the withstand voltage. Such a
design, however, lowers the output and efficiency of the
permanent-magnet-type rotating electrical machine in a low-speed
zone.
If a variable-speed operation is carried out in such a way as to
provide nearly a constant output from low speed to high speed, the
voltage of the rotating electrical machine will reach a source
voltage upper limit in a high rotation speed zone. This is because
the linkage flux of the permanent magnets is constant. In the high
rotation speed zone, therefore, a current necessary for providing
the output will not be passed. This greatly drops the output in the
high rotation speed zone and the variable-speed operation will not
be carried out in a wide range up to high rotation speed. To cope
with this, recent techniques of expanding a variable-speed range
employ flux-weakening control described in the above-mentioned
"Design and Control of Internal Magnet Synchronous Motor." The
flux-weakening control applies a demagnetizing field created with a
d-axis current to the high-coercive-force permanent magnets 4, to
move a magnetic operating point of the permanent magnets within a
reversible range and change a flux amount. Accordingly, the
internal-magnet-type rotating electrical machine performing the
field-weakening control employs as an internal permanent magnet an
NdFeB magnet that has a high coercive force and is not irreversibly
demagnetized by the demagnetizing field.
The demagnetizing field created with a d-axis current decreases the
linkage flux of the permanent magnets and the reduction in the
linkage flux produces a voltage margin for the source voltage upper
limit. This results in increasing a current to increase output in
the high-speed zone. The voltage margin also allows rotation speed
to be increased, to expand a variable speed operating range.
This technique, however, must continuously apply the demagnetizing
field to the permanent magnets. For this, a d-axis current that
contributes nothing to an output must always be passed, to increase
an iron loss and deteriorate efficiency. In addition, the
demagnetizing field produced by a d-axis current generates harmonic
flux that causes a voltage increase. Such a voltage increase limits
the voltage reduction achieved by the flux-weakening control. These
factors make it difficult for the flux-weakening control to conduct
a variable-speed operation of the internal-magnet-type rotating
electrical machine at speeds over three times a base speed. In
addition, the harmonic flux increases an iron loss and generates an
electromagnetic force that produces vibration.
When the internal-permanent-magnet motor is applied for a drive
motor of a hybrid car, the motor rotates together with an engine
when only the engine is used to drive the hybrid car. In this case,
a voltage induced by the permanent magnets of the motor at middle
or high rotation speed exceeds a power source voltage. To cope with
this, the field-weakening control must continuously pass a d-axis
current. In this state, the motor only produces a loss to
deteriorate an overall operating efficiency.
When the internal-permanent-magnet motor is applied for a drive
motor of an electric train, the electric train sometimes carries
out a coasting operation. Then, like the above-mentioned example,
the flux-weakening control must continuously pass a d-axis current,
so that a voltage induced by the permanent magnets will not exceed
a power source voltage. In this state, the motor only produces a
loss to deteriorate an overall operating efficiency.
DISCLOSURE OF INVENTION
The present invention has been made to solve the above-mentioned
problems of the related arts and an object of the present invention
is to provide a permanent-magnet-type rotating electrical machine
capable of conducting a variable-speed operation in a wide range
from low speed to high speed, realizing high torque in a low
rotation speed zone and high output in middle and high rotation
speed zones, and improving efficiency and reliability.
A permanent-magnet-type rotating electrical machine according to
the present invention is characterized in that it includes a stator
provided with a stator coil and a rotor having a rotor core in
which there are arranged a low-coercive-force permanent magnet
whose coercive force is of such a level that a magnetic field
created by a current of the stator coil may irreversibly change the
flux density of the magnet and a high-coercive-force permanent
magnet whose coercive force is equal to or larger than twice that
of the low-coercive-force permanent magnet.
The present invention can provide the permanent-magnet-type
rotating electrical machine capable of conducting a variable-speed
operation in a wide range from low speed to high speed, realizing
high torque in a low rotation speed zone and high output in middle
and high rotation speed zones, and improving efficiency and
reliability.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a sectional view illustrating a permanent-magnet-type
rotating electrical machine according to a first embodiment of the
present invention.
FIG. 2 is a sectional view illustrating a rotor of the
permanent-magnet-type rotating electrical machine according to the
first embodiment of the present invention.
FIG. 3 is a view illustrating the magnetic characteristics of low-
and high-coercive-force permanent magnets used by the first
embodiment of the present invention.
FIG. 4 is a sectional view illustrating flux of permanent magnets
in an initial state of the rotor according to the first embodiment
of the present invention.
FIG. 5 is a sectional view illustrating flux of a magnetizing field
created by a d-axis current in the rotor according to the first
embodiment of the present invention.
FIG. 6 is a sectional view illustrating flux after the action of
the magnetizing field created by the d-axis current in the rotor
according to the first embodiment of the present invention.
FIG. 7 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to an
eighth embodiment of the present invention.
FIG. 8 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
ninth embodiment of the present invention.
FIG. 9 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
tenth embodiment of the present invention.
FIG. 10 is a view illustrating a torque change with respect to a
pole central angle .alpha. according to the tenth embodiment of the
present invention.
FIG. 11 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
twelfth embodiment of the present invention.
FIG. 12 is a longitudinal sectional view illustrating a
low-coercive-force permanent magnet according to the twelfth
embodiment of the present invention.
FIG. 13 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
thirteenth embodiment of the present invention.
FIG. 14 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
fourteenth embodiment of the present invention.
FIG. 15 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
fifteenth embodiment of the present invention.
FIG. 16A is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
sixteenth embodiment of the present invention.
FIG. 16B is a sectional view illustrating the permanent-magnet-type
rotating electrical machine according to the sixteenth embodiment
of the present invention.
FIG. 17 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to a
seventeenth embodiment of the present invention.
FIG. 18 is a sectional view illustrating a rotor of a
permanent-magnet-type rotating electrical machine according to an
eighteenth embodiment of the present invention.
FIG. 19 is a sectional view illustrating a rotor of an
internal-permanent-magnet motor according to a related art.
BEST MODE OF IMPLEMENTING INVENTION
The embodiments of the present invention will be explained in
detail with reference to the drawings.
First Embodiment
As illustrated in FIGS. 1 and 2, a permanent-magnet-type rotating
electrical machine 20 according to the first embodiment of the
present invention has a rotor 1. The rotor 1 has a rotor core 2 in
which eight low-coercive-force permanent magnets 3 and eight
high-coercive-force permanent magnets 4 are embedded at equal
pitches. At a location of the rotor core 2 where the
low-coercive-force permanent magnet 3 is embedded, a first hollow 5
is formed at each end of the permanent magnet 3. At a location of
the rotor core 2 where the high-coercive-force permanent magnet 4
is embedded, a second hollow 6 is formed at each end of the
permanent magnet 4. "7" indicates a magnetic pole portion of the
rotor core 2. The rotor core 2 is constituted by laminating silicon
steel plates. The low-coercive-force permanent magnet 3 is an
alnico magnet or a FeCrCo magnet. The high-coercive-force magnet 4
is an NdFeB magnet.
As illustrated in FIG. 1, a stator 23 is constituted by winding a
stator coil 21 along inner teeth of a stator core 24. The rotor 1
is accommodated in an inner space of the stator core 24 of the
stator 23, to form the permanent-magnet-type rotating electrical
machine 20 of the embodiment. An inner circumferential face of the
stator core 24 faces an outer circumferential face of the rotor 1
with an air gap 22 interposing between them.
FIG. 3 shows the magnetic characteristics of an alnico (AlNiCo)
magnet serving as the low-coercive-force permanent magnet of the
rotor 1 adopted by the embodiment, an FeCrCo magnet that is a
low-coercive-force magnet, and an NdFeB magnet serving as the
high-coercive-force permanent magnet. The coercive force (a
magnetic field where a flux density becomes zero) of the alnico
magnet is 60 to 120 kA/m and is 1/15 to 1/8 of a coercive force of
950 kA/m of the NdFeB magnet. The coercive force of the FeCrCo
magnet is about 60 kA/m which is 1/15 of the coercive force of 950
kA/m of the NdFeB magnet. It is understood that the alnico magnet
and FeCrCo magnet each have a coercive force fairly lower than the
NdFeB magnet. According to the embodiment, the high-coercive-force
permanent magnet 4 has a coercive force 8 to 15 times higher than
that of the low-coercive-force permanent magnet 3, to provide the
rotating electrical machine with excellent characteristics.
Each low-coercive-force permanent magnet 3 is embedded in the rotor
core 2 and each end of the low-coercive-force permanent magnet 3 is
provided with the first hollow 5. The low-coercive-force permanent
magnet 3 is arranged in a radial direction of the rotor that agrees
with a q-axis serving as an inter-polar center axis and is
magnetized in a direction orthogonal to the radial direction. Each
high-coercive-force permanent magnet 4 is embedded in the rotor
core 2 and each end of the high-coercive-force permanent magnet 4
is provided with the second hollow 6. The high-coercive-force
permanent magnet 4 is arranged on the inner circumferential side of
the rotor 1 between two low-coercive-force permanent magnets 3 and
is oriented in a circumferential direction of the rotor 1. The
high-coercive-force permanent magnet 4 is magnetized in a direction
orthogonal to the circumferential direction of the rotor 1.
Each magnetic pole portion 7 of the rotor core 2 is surrounded by
two low-coercive-force permanent magnets 3 and one
high-coercive-force permanent magnet 4. As shown in FIG. 4, a
center axis of the magnetic pole portion 7 of the rotor core 2
agrees with a d-axis and an inter-polar center axis agrees with a
q-axis. The low-coercive-force permanent magnet 3 is arranged in
the direction of the q-axis serving as the inter-polar center axis
and is magnetized in a direction that forms 90.degree. or
-90.degree. with respect to the q-axis. The faces of adjacent
low-coercive-force permanent magnets 3 that face each other have
the same polarity. The high-coercive-force permanent magnet 4 is
arranged in a direction orthogonal to the d-axis serving as the
center axis of the magnetic pole portion 7 and is magnetized in a
direction that forms 0.degree. or 180.degree. with respect to the
d-axis. The magnetic pole portions 7 related to adjacent
high-coercive-force permanent magnets 4 are oppositely
polarized.
In the rotor 1 of the embodiment, the FeCrCo magnet or alnico
magnet adopted for the low-coercive-force permanent magnet 3 has a
low coercive force of 60 to 120 kA/m. Such a low-coercive-force
magnet can be magnetized with a magnetic field of 200 to 300 kA/m.
The NdFeB magnet adopted for the high-coercive-force permanent
magnet 4 has a high coercive force of 950 kA/m and is magnetized
with a magnetic field of about 2400 kA/m. Namely, the
low-coercive-force permanent magnet 3 is magnetized with a magnetic
field of about 1/10 of that for magnetizing the high-coercive-force
permanent magnet 4. The permanent-magnet-type rotating electrical
machine 20 adopting the rotor 1 of the embodiment passes a pulse
current to the stator coil for a very short time (about 100 .mu.s
to 1 ms) to form a magnetic field that acts on the
low-coercive-force permanent magnets 3. Theoretically, a
magnetizing field of 250 kA/m sufficiently magnetizes the
low-coercive-force permanent magnets 3 while no magnetization that
may cause irreversible demagnetization occurs on the
high-coercive-force permanent magnets 4.
FIG. 4 is a view illustrating fluxes B31 and B41 of the permanent
magnets 3 and 4 in an initial state before a d-axis current is
applied to produce a magnetizing field, according to the
embodiment. FIG. 5 is a view illustrating fluxes B32 and B42 of the
permanent magnets 3 and 4 when a magnetizing field is applied.
Although FIGS. 4 and 5 illustrate a flux distribution for one pole,
the same flux distribution occurs on each of the four poles. The
pulse current that forms the magnetizing field is a d-axis current
component of the armature coil of the stator. In FIG. 5, each
low-coercive-force permanent magnet 3 is demagnetized. Namely, a
negative d-axis current forms a demagnetizing field that acts from
the polar center of the rotor 1 toward the low- and
high-coercive-force permanent magnets 3 and 4 oppositely to the
magnetizing direction. In the permanent-magnet-type rotating
electrical machine 20 employing the rotor 1 of the embodiment, the
magnetic field Bd created by the d-axis current acts on two
high-coercive-force permanent magnets 4 (two permanent magnets of
N. and S. poles). Accordingly, the magnetic field acting on the
high-coercive-force permanent magnet 4 is about half the magnetic
field acting on the low-coercive-force permanent magnet 3. As a
result, in the permanent-magnet-type rotating electrical machine
employing the rotor 1 of the embodiment, the magnetic field Bd
created by the d-axis current easily magnetizes the
low-coercive-force permanent magnets 3.
FIG. 6 is a view illustrating fluxes B33 and B43 after
magnetization of the rotor 1 according to the embodiment. The
low-coercive-force permanent magnet 3 has a coercive force of about
1/10 of that of the high-coercive-force permanent magnet 4 and
receives a magnetizing field of two times as large as that acting
on the high-coercive-force permanent magnet 4. In FIG. 6, the
low-coercive-force permanent magnet 3 is magnetized in a direction
opposite to the initial magnetizing direction of FIG. 4. The
magnitude of the d-axis current can be changed to change the
strength of the magnetizing field, thereby adjusting the magnetized
state of the low-coercive-force permanent magnet 3. Namely, it is
possible to establish three states, i.e., a state of lowering the
magnetic force of the low-coercive-force permanent magnet 3, a
state of zeroing the flux of the low-coercive-force permanent
magnet 3, and a state of reversing the flux direction of the
low-coercive-force permanent magnet 3. On the other hand, the
high-coercive-force permanent magnet 4 has a coercive force 10
times as large as that of the low-coercive-force permanent magnet 3
or larger, and according to the embodiment, receives a magnetizing
field of 1/2 of that acting on the low-coercive-force permanent
magnet 3. Accordingly, a magnetic field that magnetizes the
low-coercive-force permanent magnet 3 keeps the high-coercive-force
permanent magnet 4 in a reversible demagnetization state, so that
the high-coercive-force permanent magnet 4 may maintain the initial
flux even after magnetization.
With the above-mentioned configuration, the permanent-magnet-type
rotating electrical machine employing the rotor 1 of the embodiment
can widely change a linkage flux amount of the low-coercive-force
permanent magnet 3 with a d-axis current of the rotor 1 and can
reverse the magnetizing direction thereof. With linkage flux of the
high-coercive-force permanent magnet 4 being in a normal direction,
linkage flux of the low-coercive-force permanent magnet 3 is
adjustable in a wide range from a maximum value in the normal
direction to zero to a maximum value in the opposite direction.
Accordingly, the rotor 1 of the embodiment can adjust the total
linkage flux amount of the low- and high-coercive-force permanent
magnets 3 and 4 in a wide range by magnetizing each
low-coercive-force permanent magnet 3 with a d-axis current.
For example, in a low-speed zone, the low-coercive-force permanent
magnet 3 is magnetized with a d-axis current so that the permanent
magnet 3 takes a maximum flux amount in the same direction (initial
state) as the direction of the linkage flux of the
high-coercive-force permanent magnet 4, to maximize torque produced
by the permanent magnets, thereby maximizing the torque and output
of the rotating electrical machine.
In middle- and high-speed zones, the flux amount of the
low-coercive-force permanent magnet 3 is decreased as shown in FIG.
6, to decrease the total linkage flux amount. This results in
decreasing the voltage of the rotating electrical machine, to make
a margin for a source voltage upper limit. This enables rotation
speed (frequency) to be increased further.
To further increase the maximum speed (to expand a variable-speed
range, for example, five times a base speed or more), the
low-coercive-force permanent magnet 3 is magnetized in a direction
opposite to the linkage flux of the high-coercive-force permanent
magnet 4 (the flux direction is as illustrated in FIG. 6 and
magnetization is carried out to the maximum). The total linkage
flux of the permanent magnets will be minimized to the linkage flux
difference between the high-coercive-force permanent magnets 4 and
the low-coercive-force permanent magnets 3. As a result, the
voltage of the rotating electrical machine is minimized to increase
the rotation speed (frequency) to the maximum.
Adopted for the rotating electrical machine 20 illustrated in FIG.
1, the rotor 1 of the embodiment realizes a high-output
variable-speed operation in a wide range from low speed to high
speed. It passes a magnetizing current only for a very short time
when changing linkage flux. Accordingly, it can greatly reduce a
loss and improve efficiency.
To provide output, the rotating electrical machine 20 passes a
q-axis current to the stator coil 21, so that a magnetic action
between the q-axis current and the flux of the permanent magnets 3
and 4 may generate torque. At this time, the q-axis current creates
a magnetic field. For this, the low-coercive-force permanent magnet
3 is arranged along the q-axis and is magnetized in a direction
orthogonal to the q-axis. Namely, the low-coercive-force permanent
magnet 3 is magnetized orthogonal to the magnetic field created by
the q-axis current, and therefore, is little affected thereby.
Next, the action of the first and second hollows 5 and 6 will be
explained. The hollows 5 and 6 relax a stress concentration and
demagnetizing field of the rotor core 2 when a centrifugal force by
the permanent magnets acts on the rotor core 2. As illustrated in
FIG. 2, the hollows 5 and 6 provide the iron core 2 with curved
shapes to relax stress. A magnetic field produced by a current may
concentrate at each corner of the permanent magnets 3 and 4, so
that a demagnetizing field may act at the corner to irreversibly
demagnetize the corner. The hollows 5 and 6 provided for the ends
of the magnets of the rotor 1 of the embodiment can relax such a
demagnetizing field caused by a current at each end of the
permanent magnets.
The rotor 1 of the embodiment having the above-mentioned
configuration provides the following actions and effects. With
linkage flux of the high-coercive-force permanent magnets 4 being
in a normal direction, linkage flux of the low-coercive-force
permanent magnets 3 is adjustable in a wide range from a maximum
value in the normal direction to zero to a maximum value in the
opposite direction. By magnetizing the low-coercive-force permanent
magnets 3 with a d-axis current, the total linkage flux amount of
the low- and high-coercive-force permanent magnets 3 and 4 is
adjustable in a wide range. Adjusting the total linkage flux amount
of the permanent magnets in a wide range results in adjusting the
voltage of the rotating electrical machine 20 adopting the rotor 1
in a wide range. Magnetization is carried out with a pulse current
passed for a very short time, and therefore, there is no need of
continuously passing a field-weakening current, thereby greatly
reducing a loss. Eliminating the need of conducting the
conventional field-weakening control leads to generate no iron loss
due to harmonic flux. In this way, the rotor 1 of the embodiment
enables the rotating electrical machine 20 to carry out a
high-output variable-speed operation in a wide range from low speed
to high speed and improve efficiency.
In connection with a voltage induced by the permanent magnets, the
low-coercive-force permanent magnets 3 are magnetized with a d-axis
current, to reduce the total linkage flux amount of the permanent
magnets, thereby preventing electronic parts of an inverter from
being broken with the induced voltage of the permanent magnets and
improving reliability. When the rotating electrical machine 20 is
rotated under no load, the low-coercive-force permanent magnets 3
are magnetized with a d-axis current, to reduce the total linkage
flux amount of the permanent magnets, thereby greatly decreasing
the induced voltage, eliminating the need of always passing a
field-weakening current for decreasing the induced voltage, and
improving total efficiency. Although the embodiment employs eight
poles, the embodiment may employ any other number of poles. The
structure of the stator 23 is not limited to that of the
embodiment. Any stator applicable to general rotating electrical
machines is adoptable. For example, instead of the distributed coil
stator illustrated in the drawings, a concentrated coil stator may
be adopted. These matters are applicable to the other
embodiments.
Second Embodiment
A rotating electrical machine 20 according to a second embodiment
of the present invention is characterized in that, when a rotor 1
is at a highest rotation speed, a counter electromotive voltage
generated by high-coercive-force permanent magnets 4 of the rotor
is suppressed below a withstand voltage of electronic parts of an
inverter serving as a power source of the rotating electrical
machine.
A counter electromotive voltage caused by permanent magnets
increases in proportion to rotation speed. If the counter
electromotive voltage is applied to electronic parts of an inverter
and if it exceeds a withstand voltage of the electronic parts, the
electronic parts will cause insulation breakage. For this, a
conventional permanent-magnet-type rotating electronic machine is
designed to comply with the withstand voltage by reducing the flux
amount of permanent magnets. This, however, deteriorates the output
and efficiency of the motor in a low-speed zone.
According to the rotating electrical machine 20 of the embodiment,
a negative d-axis current is applied at high-speed rotation, to
apply a magnetizing field acting in a demagnetizing direction to
the permanent magnets, thereby nearly zeroing the flux of
low-coercive-force permanent magnets 3. This nearly zeroes a
counter electromotive voltage generated by the low-coercive-force
permanent magnets 3. At the same time, a counter electromotive
voltage generated at a maximum rotation speed by the
high-coercive-force permanent magnets 4 whose flux amount is not
adjustable is restricted to be equal to or lower than the withstand
voltage. Namely, the flux amount of only the high-coercive-force
permanent magnets 4 is dropped below the withstand voltage. At
low-speed rotation, the linkage flux amount of the
low-coercive-force permanent magnets 3 maximally magnetized and the
high-coercive-force permanent magnets 4 will be quite larger than
that of the conventional permanent-magnet-type rotating electrical
machine.
In this way, the permanent-magnet-type rotating electrical machine
20 according to the embodiment is capable of maintaining high
output and high efficiency at low-speed rotation, suppressing a
counter electromotive voltage at high-speed rotation, and improving
reliability of the system including an inverter.
Third Embodiment
A permanent-magnet-type rotating electrical machine 20 according to
a third embodiment of the present invention is characterized in
that, with permanent magnets providing a maximum flux amount to
generate maximum torque, a flux amount of high-coercive-force
permanent magnets 4 is smaller than a maximum flux amount of
low-coercive-force permanent magnets 3.
When the rotating electrical machine provides the maximum torque,
the flux amount of the low- and high-coercive-force permanent
magnets 3 and 4 of a rotor 1 is maximized to reduce a necessary
current and improve efficiency. At a maximum rotation speed, a
d-axis current is passed to generate a magnetizing field to nearly
zero the flux amount of each low-coercive-force permanent magnet 3,
thereby nearly zeroing a counter electromotive voltage caused by
the low-coercive-force permanent magnets 3. At the same time, each
high-coercive-force permanent magnet 4 whose flux amount is not
adjustable is designed to suppress its counter electromotive
voltage at the maximum rotation speed lower than a withstand
voltage of electronic parts of an inverter. According to the
embodiment, the flux of the high-coercive-force permanent magnets 4
is smaller than that of the low-coercive-force permanent magnets 3,
to reduce a counter electromotive voltage produced by the
high-coercive-force permanent magnets 4 at a given rotation speed.
This enables the machine to operate at higher rotation speeds.
Fourth Embodiment
A fourth embodiment of the present invention is characterized in
that, in a permanent-magnet-type rotating electrical machine 20
having a configuration similar to that illustrated in FIG. 1, a
magnetic field created by a current of a stator coil is used to
magnetize low-coercive-force permanent magnets 3 in such a way as
to decrease a total linkage flux mount of the low- and
high-coercive-force permanent magnets 3 and 4 when the voltage of
the machine is close to or larger than a maximum power source
voltage at high-speed rotation. According to the embodiment, the
low-coercive-force permanent magnet 3 is an FeCrCo magnet or an
alnico magnet and the high-coercive-force permanent magnet 4 is an
NdFeB magnet.
In the permanent-magnet-type rotating electrical machine, the flux
amount of the permanent magnets is constant, and therefore, a
voltage generated by the linkage flux of the permanent magnets
increases in proportion to the rotation speed of the rotor 1. If
there is an upper limit on a power source voltage and if the
rotating electrical machine must be operated in a wide range from
low speed to high speed, the machine is unable to increase its
rotation speed once the power source voltage reaches the upper
limit. The voltage of the rotating electrical machine is determined
by a coil inductance and the linkage flux of the permanent magnets,
and therefore, reducing the linkage flux amount of the permanent
magnets will be effective to suppress a voltage increase at
high-speed rotation.
The embodiment employs, as the low-coercive-force permanent magnet
3, an FeCrCo magnet or an alnico magnet that has a low coercive
force such as 60 to 200kA/m and is magnetized with a magnetic field
of 200 to 300 kA/m, and as the high-coercive-force permanent magnet
4, an NdFeB magnet that has a high coercive force such as 950 kA/m
and is magnetized with a magnetic field of 2400 kA/m. The
low-coercive-force permanent magnet 3 can be magnetized with a
magnetic field of about 1/10 of that for magnetizing the
high-coercive-force permanent magnet 4. According to the
embodiment, a stator coil 21 passes a pulse current for a very
short time (about 100 .mu.s to 1 ms) to form a magnetic field
acting on the low-coercive-force permanent magnets 3. If the
magnetizing field is of 250 kA/m, a sufficient magnetic field acts,
theoretically, on the low-coercive-force permanent magnets 3. At
this time, the high-coercive-force permanent magnets 4 are not
irreversibly demagnetized due to the magnetization.
In an initial state, the linkage flux of the low-coercive-force
permanent magnets 3 and the linkage flux of the high-coercive-force
permanent magnets 4 are additional to each other, to increase the
total linkage flux. When the rotating electrical machine is
operated at high speed so that the voltage of the machine reaches
or exceeds the maximum source voltage, a negative d-axis pulse
current is passed to generate a magnetic field in a direction
opposite to the magnetizing direction of the low-coercive-force
permanent magnet 3 as illustrated in FIG. 5. Then, the
low-coercive-force permanent magnets 3 are demagnetized or are
oppositely magnetized as illustrated in FIG. 6. This results in
reducing the total linkage flux of the low- and high-coercive-force
permanent magnets 3 and 4. Reducing the total linkage flux amount
decreases the voltage of the rotating electrical machine below the
source voltage upper limit. Then, the rotation speed of the
rotating electrical machine can further be increased until the
source voltage reaches the upper limit.
Changing the magnitude of a d-axis current results in changing the
strength of a magnetizing field and changing the magnetized state
of each low-coercive-force permanent magnet 3. This results in
adjusting a voltage. At this time, the low-coercive-force permanent
magnets 3 are changeable among three states including a state of
lowering a magnetic force, a state of zeroing the flux of the
low-coercive-force permanent magnets, and a state of reversing the
direction of the flux of the low-coercive-force permanent
magnets.
On the other hand, the high-coercive-force permanent magnet 4 has a
coercive force 10 times as large as that of the low-coercive-force
permanent magnet 3 or larger. According to the embodiment, a
magnetizing field acting on the high-coercive-force permanent
magnet 4 is 1/2 of that acting on the low-coercive-force permanent
magnet 3. Accordingly, a magnetic field that is sufficient to
magnetize the low-coercive-force permanent magnets 3 keeps the
high-coercive-force permanent magnets 4 in an irreversibly
demagnetized state, so that the high-coercive-force permanent
magnets can maintain the flux of the initial state even after
magnetization.
When providing output, the stator coil passes a q-axis current to
generate torque with a magnetic action between the q-axis current
and the flux of the permanent magnets. At this time, the q-axis
current generates a magnetic field. However, each
low-coercive-force permanent magnet 3 is arranged in the q-axis
direction and is magnetized in a direction orthogonal to the q-axis
direction. Namely, the magnetizing direction of each
low-coercive-force permanent magnet is orthogonal to the magnetic
field created by the q-axis current. Accordingly, the influence of
the magnetic field created by the q-axis current is minor.
Fifth Embodiment
A fifth embodiment of the present invention is characterized in
that, when a permanent-magnet-type rotating electrical machine
having a configuration similar to that illustrated in FIG. 1 is
operating at low speed with the voltage thereof being lower than a
maximum source voltage, each low-coercive-force permanent magnet 3
is magnetized with a magnetic field created by a current of a
stator coil in such a way as to increase the linkage flux of the
low- and high-coercive-force permanent magnets 3 and 4, and when
the rotating electrical machine is operating at high speed with the
voltage thereof being around or above the maximum source voltage,
each low-coercive-force permanent magnet 3 is magnetized with a
magnetic field created by a current of the stator coil in such a
way as to decrease the linkage flux of the low- and
high-coercive-force permanent magnets 3 and 4. The embodiment
adjusts the linkage flux amount of the permanent magnets in this
way.
According to the embodiment, the low-coercive-force permanent
magnet 3 is an FeCrCo magnet or an alnico magnet and the
high-coercive-force permanent magnet 4 is an NdFeB magnet. The
FeCrCo magnet or alnico magnet used as the low-coercive-force
permanent magnet 3 of the embodiment has a low coercive force such
as 60 to 200 kA/m and is magnetized with a magnetic field of 200 to
300 kA/m. The NdFeB magnet used as the high-coercive-force
permanent magnet 4 has a high coercive force such as 950 kA/m and
is magnetized with a magnetic field of 2400 kA/m. Namely, the
low-coercive-force permanent magnet 3 can be magnetized with a
magnetic field of about 1/10 of that for magnetizing the
high-coercive-force permanent magnet 4. According to the
embodiment, the stator coil passes a pulse current for a very short
time (about 100 .mu.s to 1 ms) to form a magnetic field acting on
the low-coercive-force permanent magnets 3. If the magnetizing
field is of 250 kA/m, a sufficient magnetic field acts,
theoretically, on each low-coercive-force permanent magnet 3. At
this time, each high-coercive-force permanent magnet 4 is not
irreversibly demagnetized due to the magnetization.
When the rotating electrical machine is operating at low speed with
the voltage of the machine having a margin with respect to a
maximum source voltage, a positive d-axis current is passed to
generate a magnetizing field that magnetizes the low-coercive-force
permanent magnets 3. The linkage flux of the low-coercive-force
permanent magnets 3 is in the same direction as the linkage flux of
the high-coercive force permanent magnets 4, to increase the total
linkage flux. The total linkage flux of the permanent magnets and a
q-axis current together generate torque. Namely, the increased
linkage flux of the permanent magnets increases torque.
When the rotating electrical machine is operating at high speed
with the voltage of the machine being close to or above the maximum
source voltage, each low-coercive-force permanent magnet 3 is
magnetized with a magnetic field created by a current of the stator
coil in such a way as to decrease the linkage flux of the low- and
high-coercive-force permanent magnets 3 and 4, thereby adjusting
the linkage flux amount of the permanent magnets like the fourth
embodiment. Reducing the linkage flux amount decreases the voltage
of the rotating electrical machine below the maximum source
voltage, and therefore, the machine can be operated at higher
speeds until the maximum source voltage is attained.
In this way, the rotating electrical machine of the embodiment
generates a magnetic field with a d-axis current serving as a
magnetizing current, adjusts the linkage flux amount of each
low-coercive-force permanent magnet 3 with the d-axis current,
generates high torque at low speed, achieves a high-output
high-speed operation, and realizes a high-output variable-speed
operation in a wide range from low speed to high speed.
Sixth Embodiment
A sixth embodiment of the present invention is characterized in
that a permanent-magnet-type rotating electrical machine 20 having
a configuration similar to that illustrated in FIG. 1 passes a
d-axis current through a stator coil 21, to form a magnetic field
that adjusts the flux amount of each low-coercive-force permanent
magnet 3 so that the linkage flux amount of the low- and
high-coercive-force permanent magnets 3 and 4 is zeroed.
According to the embodiment, the low-coercive-force permanent
magnet 3 is an FeCrCo magnet or an alnico magnet and the
high-coercive-force permanent magnet 4 is an NdFeB magnet. The
FeCrCo magnet or alnico magnet used as the low-coercive-force
permanent magnet 3 of the embodiment has a low coercive force such
as 60 to 200 kA/m and is magnetized with a magnetic field of 200 to
300 kA/m. The NdFeB magnet used as the high-coercive-force
permanent magnet 4 has a high coercive force such as 950 kA/m and
is magnetized with a magnetic field of 2400 kA/m. Namely, the
low-coercive-force permanent magnet 3 can be magnetized with a
magnetic field of about 1/10 of that for magnetizing the
high-coercive-force permanent magnet 4.
According to the embodiment, the stator coil passes a pulse current
for a very short time (about 100 .mu.s to 1 ms) to form a magnetic
field acting on the low-coercive-force permanent magnets 3. If the
magnetizing field is of 250 kA/m, a sufficient magnetic field acts,
theoretically, on each low-coercive-force permanent magnet 3. At
this time, each high-coercive-force permanent magnet 4 is not
magnetized, and when the pulse current becomes zero, reversibly
changes to an original state. Namely, the linkage flux amount of
the low-coercive-force permanent magnet 3 is adjusted and that of
the high-coercive-force permanent magnet 4 is constant.
A d-axis current is passed to generate a magnetizing field that
adjusts the flux amount of the low-coercive-force permanent magnets
3 so as to zero the linkage flux amount of the low- and
high-coercive-force permanent magnets 3 and 4. Since the linkage
flux of the permanent magnets is zeroed, no iron loss will occur
due to the linkage flux of the permanent magnets when the rotating
electrical machine is externally turned. In the case of a permanent
magnet motor according to a related art applied to a system for
driving a hybrid vehicle or an electric train, a voltage induced by
permanent magnets at high rotation speed will break electronic
parts of an inverter if the voltage exceeds a withstand voltage of
the electronic parts. To keep the voltage of the motor lower than a
power source voltage, the related art must always pass a
field-weakening current in a high-speed zone even under no load.
This deteriorates the total efficiency of the motor.
In the case of the permanent-magnet-type rotating electrical
machine of the embodiment applied to a system for driving a hybrid
vehicle or an electric train, it is possible to zero the linkage
flux of the permanent magnets, so that a voltage induced by the
permanent magnets will not break the electronic parts of an
inverter and there is no need of always passing a field-weakening
current in a high-speed zone under no load. Accordingly, the
rotating electrical machine of the embodiment improves the
reliability and efficiency of the system.
Seventh Embodiment
A seventh embodiment of the present invention is characterized in
that a permanent-magnet-type rotating electrical machine 20 having
a configuration similar to that illustrated in FIG. 1 equalizes,
when a maximum flux amount is obtained due to magnetization with a
d-axis current, a flux amount of low-coercive-force permanent
magnets 3 with a flux amount of high-coercive-force permanent
magnets 4.
According to the embodiment, the low-coercive-force permanent
magnet 3 is an FeCrCo magnet or an alnico magnet and the
high-coercive-force permanent magnet 4 is an NdFeB magnet.
The FeCrCo magnet or alnico magnet used as the low-coercive-force
permanent magnet 3 of the embodiment has a low coercive force such
as 60 to 200 kA/m and is magnetized with a magnetic field of 200 to
300 kA/m. The NdFeB magnet used as the high-coercive-force
permanent magnet 4 has a high coercive force such as 950 kA/m and
is magnetized with a magnetic field of 2400 kA/m. Namely, the
low-coercive-force permanent magnet 3 can be magnetized with a
magnetic field of about 1/10 of that for magnetizing the
high-coercive-force permanent magnet 4.
According to the embodiment, a stator coil passes a pulse current
for a very short time (about 100 .mu.s to 1 ms) to form a magnetic
field acting on the low-coercive-force permanent magnets 3. If the
magnetizing field is of 250 kA/m, a sufficient magnetic field acts,
theoretically, on each low-coercive-force permanent magnet 3. At
this time, each high-coercive-force permanent magnet 4 is not
magnetized, and when the pulse current becomes zero, reversibly
changes to an original state. Namely, the linkage flux amount of
the low-coercive-force permanent magnets 3 is adjusted and that of
the high-coercive-force permanent magnets 4 is unchanged.
As explained in the sixth embodiment, zeroing the linkage flux
amount of the permanent magnets improves the reliability and
efficiency of a system that employs the rotating electrical
machine. For this, a d-axis current is passed to generate a
magnetizing field that adjusts the flux amount of the
low-coercive-force permanent magnets 3 so that the linkage flux
amount of the low- and high-coercive-force permanent magnets 3 and
4 is zeroed.
The seventh embodiment equalizes a flux amount of the
low-coercive-force permanent magnets 3 with a flux amount of the
high-coercive-force permanent magnets 4. The magnetizing direction
of each low-coercive-force permanent magnet 3 is set to generate
linkage flux in an opposite direction to linkage flux of each
high-coercive-force permanent magnet 4 and the low-coercive-force
permanent magnet 3 is completely magnetized with a magnetizing
field of 250 kA/m or over. Namely, only by creating a magnetizing
field of 250 kA/m or over, the total linkage flux amount of the
permanent magnets can surely and easily be zeroed without regard to
fluctuations in a magnetizing current and ambient conditions such
as temperature.
Eighth Embodiment
FIG. 7 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to an
eighth embodiment of the present invention. The same or equal
elements as those of FIG. 2 are illustrated with the same reference
marks. The rotor 1 illustrated in FIG. 7 has a rotor core 2 in
which low-coercive-force permanent magnets 3 and
high-coercive-force permanent magnets 4 are embedded at equal
pitches. Except for a part around an end of each low-coercive-force
permanent magnet 3, the rotor core 2 on an air gap side is recessed
in the vicinity of the end of each low-coercive-force permanent
magnet 3 from an outermost circumference of the rotor core 2, to
form a recess B. In the rotor core 2, each end of the part where
the low-coercive-force permanent magnet 3 is embedded is provided
with a first hollow 5 and each end of the part where the
high-coercive-force permanent magnet 4 is embedded is provided with
a second hollow 6. "7" indicates a magnetic pole portion of the
rotor core 2.
Action of the rotor 1 of the embodiment will be explained. The
permanent-magnet-type rotating electrical machine 20 employing the
rotor 1 is configured like that illustrated in FIG. 1. In such a
rotating electrical machine 20, flux (d-axis flux) created by a
d-axis current crosses the low- and high-coercive-force permanent
magnets 3 and 4. The magnetic permeability of the permanent magnets
is substantially equal to that of air, and therefore, a d-axis
inductance is small. On the other hand, flux in a q-axis direction
passes through the pole portion 7 of the rotor core 2 along the
low- and high-coercive-force permanent magnets 3 and 4. The
magnetic permeability of the pole portion 7 of the rotor core 2 is
1000 to 10000 times as large as that of the permanent magnets. If
the q-axis part of the rotor core 2 has no recess and if the outer
diameter of the rotor core 2 is circumferentially uniform, a q-axis
inductance will be large. A q-axis current is passed to generate
torque with magnetic action of the current and flux. At this time,
the large q-axis inductance increases a voltage generated by the
q-axis current, thereby deteriorating a power factor.
To cope with this, the embodiment forms the recess 8 on the
outermost circumference of the rotor core 2 around an end of each
low-coercive-force permanent magnet 3 on the air gap side, to
reduce flux passing through the recesses 8 of the rotor core 2.
Since the recess 8 is in the q-axis direction, the q-axis
inductance is reduced to improve a power factor. Each recess 8
equivalently elongates an air gap length around each end of the
low-coercive-force permanent magnet 3, to lower an average magnetic
field around the end of the low-coercive-force permanent magnet 3.
This results in reducing the influence of a demagnetizing field on
the low-coercive-force permanent magnet 3 due to the q-axis current
for generating torque.
A part of the rotor core that is at an end of each
low-coercive-force permanent magnet 3 and supports the permanent
magnet is not recessed, and therefore, the diametrical length of
the low-coercive-force permanent magnet 3 can be extended as long
as possible, so that the volume of the permanent magnet is secured
compared to a rotor having the same diameter. Namely, the
embodiment can increase the flux amount of the permanent magnets
and increase output per rotor volume.
Ninth Embodiment
FIG. 8 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
ninth embodiment of the present invention. The same or equal
elements as those of FIGS. 2 and 7 are illustrated with the same
reference marks. In FIG. 8, the rotor 1 has a rotor core 2 in which
low-coercive-force permanent magnets 3 and high-coercive-force
permanent magnets 4 are embedded at equal pitches. Each end of the
low-coercive-force permanent magnet 3 is provided with a first
hollow 5 and each end of the high-coercive-force permanent magnet 4
is provided with a second hollow 6. "7" indicates a magnetic pole
portion of the rotor core 2.
The low-coercive-force permanent magnet 3 is arranged in a radial
direction on a q-axis serving as a center axis of an inter-polar
part between adjacent pole portions 7. Between an end of the
low-coercive-force permanent magnet 3 and the middle of the
magnetic pole portion 7 of the rotor core 2, the middle of the
magnetic pole portion 7 of the rotor core 2 defines an outermost
circumferential part of the rotor 1. From the middle of the
magnetic pole portion 7 toward the outer circumference of the rotor
core at the end of the low-coercive-force permanent magnet 3, the
distance between an axial center of the rotor 1 and the outer
circumference of the rotor core 2 is gradually shortened, to form
the recess 8.
Action of the rotor 1 having the above-mentioned configuration will
be explained. The permanent-magnet-type rotating electrical machine
20 employing the rotor 1 is the same as that illustrated in FIG. 1.
In the rotating electrical machine 20, flux (d-axis flux) created
by a d-axis current crosses the low- and high-coercive-force
permanent magnets 3 and 4 of the rotor 1. The magnetic permeability
of the permanent magnets is substantially equal to that of air, and
therefore, a d-axis inductance is small. On the other hand, flux in
a q-axis direction passes through the pole portion 7 of the rotor
core along the low- and high-coercive-force permanent magnets 3 and
4.
The magnetic permeability of the pole portion 7 is 1000 to 10000
times as large as that of the magnets. If the rotor core 2 has no
recess 8 in the q-axis direction and if the outer diameter of the
rotor core is circumferentially uniform, a q-axis inductance will
be large. A q-axis current is passed to generate torque with
magnetic action of the current and flux. At this time, the large
q-axis inductance increases a voltage generated by the q-axis
current. Therefore, if the rotor core has no recess 8 in the q-axis
direction and if the outer diameter of the rotor core is
circumferentially uniform, the large q-axis inductance deteriorates
a power factor.
To cope with this, the embodiment gradually shortens the distance
between the axial center of the rotor 1 and the outer circumference
of the rotor core 2 from the middle of the outer circumference of
the pole portion 7 toward the outer circumference of the rotor core
at the end of the low-coercive-force permanent magnet 3. In the
permanent-magnet-type rotating electrical machine employing the
rotor 1, each recess 8 on the rotor core on the air gap side
gradually deepens from the middle of the pole portion 7 toward the
end of the low-coercive-force permanent magnet 3. The recess 8 of
this shape elongates an air gap length, to reduce flux passing
through the recess 8 as the recess 8 deepens. Since the recess 8 is
in the q-axis direction, it can reduce the q-axis inductance.
Reducing the q-axis inductance results in improving a power factor.
The recess is deepest around the end of the low-coercive-force
permanent magnet 3 that is on the q-axis, to effectively reduce the
q-axis inductance.
Due to the recess 8, the air gap length of the rotating electrical
machine 20 becomes longest at the end of the low-coercive-force
permanent magnet 3, and therefore, a magnetic field around the end
of the low-coercive-force permanent magnet 3 decreases. This
reduces the influence of a q-axis current used for generating
torque on a demagnetizing field that acts on the low-coercive-force
permanent magnet.
Tenth Embodiment
FIG. 9 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
tenth embodiment of the present invention. The same or equivalent
elements as those of FIGS. 2, 7, and 8 are illustrated with the
same reference marks. In FIG. 9, the rotor 1 has a rotor core 2 in
which low-coercive-force permanent magnets 3 and
high-coercive-force permanent magnets 4 are embedded at equal
pitches. Each end of the low-coercive-force permanent magnet 3 is
provided with a first hollow 5 and each end of the
high-coercive-force permanent magnet 4 is provided with a second
hollow 6. A part of the rotor core 2 corresponding to an outer end
of the low-coercive-force permanent magnet 3 is recessed to form a
recess 8. "7" indicates a magnetic pole portion of the rotor core
2. ".alpha." is a central angle of a circular arc at a middle of
the magnetic pole portion 7 of the rotor core 2.
The middle of the magnetic pole portion 7 of the rotor core 2 is
formed with the circular arc defined with a maximum radius of the
rotor 1 (the maximum length from the central axis of the rotor to
the outer circumference of the rotor). The central angle .alpha. of
the circular arc at the middle of the pole portion is within a
range of 90 to 140 degrees in electrical angle. In an area outside
the central angle .alpha. of the rotor core 2, the recess 8 is
formed by recessing the outer circumference of the rotor core 2
from the circular arc having the maximum radius toward an inner
circumferential side.
The permanent-magnet-type rotating electrical machine 20 employing
the rotor 1 has substantially the same configuration as that
illustrated in FIG. 1. When the rotating electrical machine 20 is
operated in low- and middle-speed zones with the voltage thereof
being below a maximum source voltage, the flux of the permanent
magnets is maximally used to improve efficiency. According to the
embodiment, the middle of the magnetic pole portion 7 of the rotor
core 2 defined by the central angle .alpha. is formed with the
circular arc having the maximum radius of the rotor 1, and
therefore, an air gap length around a d-axis, which is present at
this location, is shortest. Accordingly, the middle part having the
central angle .alpha. around the d-axis involves a large linkage
flux amount of the high- and low-coercive-force permanent magnets 4
and 3.
Around a q-axis along which the low-coercive-force permanent magnet
3 is arranged, the outer circumference of the rotor core 2 is
recessed inwardly from the circular arc having the maximum radius
of the rotor 1. As a result, a magnetic field produced by a q-axis
current is weak. When a q-axis current is passed to generate
torque, this configuration prevents each low-coercive-force
permanent magnet 3 from demagnetizing due to a magnetic field
created by the q-axis current.
With the above-mentioned configuration, the permanent-magnet-type
rotating electrical machine 20 employing the rotor 1 of the
embodiment increases the flux amount of the permanent magnets
around the d-axis, to secure high output and high torque. At the
same time, the machine greatly reduces the influence of a q-axis
current on the demagnetization of the low-coercive-force permanent
magnets 3.
FIG. 10 is a view illustrating changes in torque with respect to
the central angle .alpha. of the permanent-magnet-type rotating
electrical machine according to the embodiment. It is understood
that, when the central angle .alpha. of the circular arc at the
middle of the pole portion is in the range of 90 to 140 degrees in
electrical angle, large torque is obtained.
Eleventh Embodiment
A permanent-magnet-type rotating electrical machine according to an
eleventh embodiment of the present invention will be explained. The
permanent-magnet-type rotating electrical machine of the embodiment
is characterized in that, based on the permanent-magnet-type
rotating electrical machine 20 of the first embodiment illustrated
in FIGS. 1 and 2, the magnetizing direction thickness of the
low-coercive-force permanent magnet 3 embedded in the rotor core 2
of the rotor 1 is thinner than the magnetizing direction thickness
of the high-coercive-force permanent magnet 4. The strength of a
magnetic field for magnetizing a permanent magnet is substantially
proportional to the magnetizing direction thickness of the
permanent magnet. Accordingly, thinning the magnetizing direction
thickness of the low-coercive-force permanent magnet 3 than the
magnetizing direction thickness of the high-coercive-force
permanent magnet 4 results in lowering a magnetic field necessary
for magnetizing the low-coercive-force permanent magnet 3 and
reducing a magnetizing current for the same.
Generally, a temperature characteristic of the high-coercive-force
permanent magnet 4 deteriorates as a magnetic energy product
increases, and at a high temperature over 100.degree. C., the
coercive force thereof drops so that the permanent magnet is
irreversibly demagnetized with a smaller demagnetizing field. To
cope with this, the embodiment decrease a magnetic field for
magnetizing the low-coercive-force permanent magnet 3, to prevent
the high-coercive-force permanent magnet 4 from being irreversibly
demagnetized when a magnetizing field is applied to the permanent
magnets in a high-temperature state.
Twelfth Embodiment
FIG. 11 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
twelfth embodiment of the present invention. The same or equivalent
parts as those of FIGS. 2 and 7 to 9 are illustrated with the same
reference marks. In FIG. 11, the rotor 1 has a rotor care 2 in
which low-coercive-force permanent magnets 3 and
high-coercive-force permanent magnets 4 are embedded at equal
pitches. Each end of the low-coercive-force permanent magnet 3 is
provided with a first hollow 5 and each end of the
high-coercive-force permanent magnet 4 is provided with a second
hollow 6. A part of the rotor core 2 corresponding to an outer end
of the low-coercive-force permanent magnet 3 is recessed to form a
recess 8. "7" indicates a magnetic pole portion of the rotor core
2. In the rotor 1 of the embodiment, the magnetizing direction
thickness of the low-coercive-force permanent magnet 3 is not
uniform but gradually increases toward the outer circumferential
side of the rotor 1.
When a magnetizing field is applied to the low-coercive-force
permanent magnet 3, the magnetizing field acting on the
low-coercive-force permanent magnet 3 in the rotor 1 is not
uniformly distributed but the strength thereof in the permanent
magnet is biased. If the magnetic field is biased to a specific
part, adjusting the flux amount of the low-coercive-force permanent
magnet 3 with a magnetizing current will be difficult. Fluctuations
in the magnetizing field or temperature during operation also
affect the flux amount of the permanent magnet. Then, it will be
difficult for the permanent magnet to secure the reproducibility of
a flux amount at the time of magnetization. To deal with this, the
embodiment utilizes the characteristic of a permanent magnet that a
magnetizing force necessary for magnetizing the permanent magnet
largely depends on the magnetizing direction thickness of the
permanent magnet.
According to the rotor 1 of the embodiment, the magnetizing
direction thickness of the low-coercive-force permanent magnet 3 is
not uniform but varies. When a magnetizing field is applied, the
permanent magnet provides different flux amounts depending on the
thicknesses thereof. Namely, the strength of a magnetizing field
becomes largely dependent on the thickness of the permanent magnet.
This configuration reduces the influence of external conditions
such as magnetic field concentration and deviation and magnetizing
field fluctuations, makes it easy to adjust a flux amount with a
magnetizing current, and minimizes flux fluctuations due to
external conditions.
FIG. 12 is a longitudinal section illustrating the
low-coercive-force permanent magnet 3 adopted by the embodiment. In
FIG. 12, the magnetizing direction thickness of the
low-coercive-force permanent magnet 3 changes in stepwise. This
shape increases the flux amount of the permanent magnet in stepwise
according to the thicknesses of the permanent magnet. The influence
of the thicknesses of the permanent magnet on the flux amount
thereof is quite larger than the influence of disturbances or
external conditions on the same. As a result, when the
low-coercive-force permanent magnet 3 is magnetized to change the
flux amount thereof, fluctuations in the flux amount caused by
fluctuations in the magnetizing field are reduced, to improve the
reproducibility of the flux amount of the low-coercive-force
permanent magnet 3 with respect to the same magnetizing
current.
Thirteenth Embodiment
FIG. 13 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
thirteenth embodiment of the present invention. The same or
equivalent parts as those of FIGS. 2, 7 to 9, and 11 are
illustrated with the same reference marks. In FIG. 13, the rotor 1
has a rotor core 2 in which low-coercive-force permanent magnets 3
and high-coercive-force permanent magnets 4 are embedded at equal
pitches. Each end of the low-coercive-force permanent magnet 3 is
provided with a first hollow 5 and each end of the
high-coercive-force permanent magnet 4 is provided with a second
hollow 6. A part of the rotor core 2 corresponding to an outer end
of the low-coercive-force permanent magnet 3 is recessed to form a
recess 8. "7" indicates a magnetic pole portion of the rotor core
2.
This embodiment is characterized in that the low-coercive-force
permanent magnet 3 has a tapered shape so that the magnetizing
direction thickness of the permanent magnet 3 gradually becomes
thinner toward the outer circumferential side of the rotor 1.
Thinning the thickness of the low-coercive-force permanent magnet 3
toward the outer circumferential side of the rotor 1 makes a face
of the rotor core that is in contact with the low-coercive-force
permanent magnet 3 receive a centrifugal force of the
low-coercive-force permanent magnet 3, so that the rotor core 2
firmly holds the low-coercive-force permanent magnet 3. Even if a
dimensional accuracy of the magnetic direction thickness of the
low-coercive-force permanent magnet 3 is rough, the
low-coercive-force permanent magnet 3 gets in contact with the
rotor core 2 at a diametrical position corresponding to the
dimensional accuracy and is fixed thereto. The embodiment is
achievable with a molding technique to mass-produce the
low-coercive-force permanent magnets with a mold.
In addition to the effects of surely holding the low-coercive-force
permanent magnets 3 and mass-producing the permanent magnets, the
embodiment provides the following actions and effects. If the
thickness of the low-coercive-force permanent magnet 3 is uniform,
there will be a problem that a magnetizing field of the
low-coercive-force permanent magnet 3 fluctuates to sharply and
partly change the flux amount of the low-coercive-force permanent
magnet. A magnetizing field of a permanent magnet is greatly
dependent on the thickness of the permanent magnet. When a
permanent magnet is magnetized, the flux amount of a part of the
permanent magnet is greatly dependent on the thickness of the part.
For this, the embodiment provides the low-coercive-force permanent
magnet 3 with different thicknesses, so that the flux amount
thereof may greatly change depending on the partial thicknesses of
the permanent magnet. Namely, the strength of a magnetic field that
determines the flux of the permanent magnet is dependent on the
thickness of the permanent magnet. The embodiment can secure a wide
variation width for a magnetizing field with respect to a variation
width of the flux amount of the low-coercive-force permanent magnet
3. Namely, by adjusting a magnetizing current in the rotating
electrical machine, the embodiment can easily adjust the flux
amount of an optional permanent magnet, to minimize fluctuations in
the flux amount of the low-coercive-force permanent magnet after
repetition of magnetization (good reproducibility) and narrow the
range of fluctuation of the flux amount of the permanent magnet
with respect to fluctuations in a magnetizing current and ambient
conditions such as temperature.
Fourteenth Embodiment
FIG. 14 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
fourteenth embodiment of the present invention. The same or
equivalent parts as those of FIGS. 2, 7 to 9, 11, and 13 are
illustrated with the same reference marks. In FIG. 14, the rotor 1
has a rotor core 2 in which low-coercive-force permanent magnets 3
and high-coercive-force permanent magnets 4 are embedded at equal
pitches. An inner end of the low-coercive-force permanent magnet 3
is provided with a first hollow 5 and each end of the
high-coercive-force permanent magnet 4 is provided with a second
hollow 6. A part of the rotor core 2 corresponding to an outer end
of the low-coercive-force permanent magnet 3 is recessed to form a
recess 8. "7" indicates a magnetic pole portion of the rotor core
2, "9" a magnetic barrier, and "10" a projection.
The rotor 1 of the embodiment has the magnetic barrier 9 formed in
the rotor core 2 around an air-gap-side end of the
low-coercive-force permanent magnet 3, the magnetic barrier being
circumferentially longer than the magnetizing direction thickness
of the low-coercive-force permanent magnet 3. The magnetic barrier
9 is a hole where air is present. On the outer-circumferential-side
(air-gap-side) end of the low-coercive-force permanent magnet 3,
there is the projection 10. The projection 10 receives a
centrifugal force of the low-coercive-force permanent magnet 3 and
holds the permanent magnet.
The rotor 1 of the embodiment is assembled in the
permanent-magnet-type rotating electrical machine 20 like the first
embodiment of FIG. 1. To generate torque for the
permanent-magnet-type rotating electrical machine 20, a q-axis
current is passed. The q-axis current generates a magnetic field on
the low-coercive-force permanent magnet 3 of the rotor 1 on the
q-axis. According to the rotor 1 of the embodiment, the magnetic
barrier 9 is arranged adjacent to an end of the low-coercive-force
permanent magnet 3, and therefore, the air layer of the magnetic
barrier 9 reduces the magnetic field created by the q-axis current
and acting on the end of the low-coercive-force permanent magnet 3.
This suppresses the demagnetization and magnetization of the
low-coercive-force permanent magnet 3 due to the q-axis current.
The magnetic barrier 9 is circumferentially longer than the
magnetizing direction thickness of the low-coercive-force permanent
magnet 3, and therefore, it can relax the magnetic field created by
the q-axis current and concentrating to the end corners of the
low-coercive-force permanent magnet 3. This prevents the
demagnetization and magnetization of the low-coercive-force
permanent magnet 3 due to the magnetic field created by the q-axis
current and sneaking around the permanent magnet. The magnetic
barrier 9 is long in the circumferential direction of the rotor
around the q-axis, to increase magnetic resistance in the q-axis
direction and reduce a flux amount due to the q-axis current. This
results in reducing a q-axis inductance and improving a power
factor.
Fifteenth Embodiment
FIG. 15 is a sectional view showing a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
fifteenth embodiment of the present invention. The same or
equivalent parts as those of FIGS. 2, 7 to 9, 11, 13, and 14 are
illustrated with the same reference marks. In FIG. 15, the rotor 1
has a rotor core 2 in which low-coercive-force permanent magnets 3
and high-coercive-force permanent magnets 4 are embedded at equal
pitches. An inner end of the low-coercive-force permanent magnet 3
is provided with a first hollow 5 and each end of the
high-coercive-force permanent magnet 4 is provided with a second
hollow 6. A part of the rotor core 2 corresponding to an outer end
of the low-coercive-force permanent magnet 3 is recessed to form a
recess 8. In FIG. 15, "7" indicates a magnetic pole portion of the
rotor core 2, "9" a magnetic barrier, and "10" a projection. This
embodiment is characterized in that a slit 11 is arranged at a
position agreeing with a d-axis that is a center axis of a pole
portion 7 of the rotor core 2 between adjacent low-coercive-force
permanent magnets 3.
The slit 11 is on the d-axis, and therefore, does not form a
magnetic barrier against d-axis flux but it serves as a magnetic
barrier against q-axis flux. Namely, the slit gives little
influence on the flux of permanent magnets distributed around the
d-axis and reduces q-axis flux. Accordingly, the
permanent-magnet-type rotating electrical machine 20 employing the
rotor 1 of the embodiment can maintain torque generated by the
permanent magnets and improve a power factor.
Sixteenth Embodiment
FIGS. 16A and 16B are sectional views illustrating a rotor 1 and
permanent-magnet-type rotating electrical machine 20 according to a
sixteenth embodiment of the present invention. The same or
equivalent parts as those of FIGS. 2, 7 to 9, 11, and 13 to 15 are
illustrated with the same reference marks. In FIG. 16A, the rotor 1
has a rotor core 2 in which low-coercive-force permanent magnets 4A
and high-coercive-force permanent magnets 3A are embedded at equal
pitches. Each end of the high-coercive-force permanent magnet 3A is
provided with a first hollow 5 and each end of the
low-coercive-force permanent magnet 4A is provided with a second
hollow 6. A part of the rotor core 2 corresponding to an outer end
of the high-coercive-force permanent magnet 3A is recessed to form
a recess 8. "7" indicates a magnetic pole portion of the rotor core
2.
Unlike the first to fifteenth embodiments, the rotor 1 of this
embodiment is characterized in that each high-coercive-force
permanent magnet 3A is arranged in a diametrical direction of the
rotor 1 and each low-coercive-force permanent magnet 4A is arranged
in a circumferential direction on the inner circumferential side of
the rotor core 2.
As illustrated in FIG. 16B, the rotor 1 of the embodiment is
accommodated, like the other embodiments, at the center of a stator
23 of the permanent-magnet-type rotating electrical machine 20, so
that the rotor 1 is driven by a magnetic field created by a stator
coil 21. A magnetic field generated by a stator current acting on
each high-coercive-force permanent magnet 3A arranged in the
diametrical direction forms a magnetic path passing through a
stator core 24, an air gap 22, the pole portion 7, the
high-coercive-force permanent magnet 3A arranged in the diametrical
direction (traversing), an adjacent pole portion 7, and the stator
core 24. On the other hand, a magnetic field generated by a stator
current acting on the low-coercive-force permanent magnet 4A
circumferentially arranged on the inner circumferential side forms
a magnetic path passing through the stator core 24, the air gap 22,
the pole portion 7, the low-coercive-force permanent magnet 4A
arranged in the circumferential direction (traversing), an
innermost circumferential part of the rotor core 2, an adjacent
innermost circumferential part of the rotor core 2, a
circumferentially adjacent low-coercive-force permanent magnet 4A
(traversing), an adjacent pole portion 7, and the stator core
24.
Accordingly, a magnetic field created by a current acts on two
circumferentially adjacent low-coercive-force permanent magnets 4A
and one diametrically arranged high-coercive-force permanent magnet
3A. If the high- and low-coercive-force permanent magnets 3A and 4A
have the same thickness, a magnetic field created by the current
and acting on the diametrically arranged high-coercive-force
permanent magnet 3A is twice as strong as that acting on the
circumferentially arranged low-coercive-force permanent magnet
4A.
A rotating electrical machine that provides high output by cooling
a stator with water or oil and increasing specific electric loading
(ampere-turn per unit circumferential length) causes a large
magnetic field due to a load current. This strong magnetic field
due to the load current causes partial demagnetization. Even if
used as such a high-output-density rotating electrical machine, the
permanent-magnet-type rotating electrical machine 20 of the
embodiment can reduce the influence of partial demagnetization
because it arranges the low-coercive-force permanent magnets 4A,
which are easily affected by a magnetic field, on the inner
circumferential side. The permanent-magnet-type rotating electrical
machine 20 of the embodiment magnetizes the permanent magnets with
a d-axis current of the rotor 1, to vary the linkage flux of the
permanent magnets, suppress changes in the characteristics of the
permanent magnets due to a load current, and maintain high
output.
According to the embodiment, the iron core recesses 8 are formed if
needed. The outer circumferential face of the rotor core 2 may have
a true circular section like the first embodiment illustrated in
FIG. 2, or any shape illustrated in FIGS. 7 and 9. The first hollow
5 may have the shape illustrated in FIGS. 14 and 15. Also, the
high-coercive-force permanent magnet 3A arranged on the outer
circumferential side may have any shape illustrated in FIGS. 12,
13, and 14.
Seventeenth Embodiment
FIG. 17 is a sectional view illustrating a rotor 1 of a
permanent-magnet-type rotating electrical machine according to a
seventeenth embodiment of the present invention. The same or
equivalent parts as those of FIGS. 2, 7 to 9, 11, and 13 to 16 are
illustrated with the same reference marks. The rotor 1 of the
embodiment is characterized in that high-coercive-force permanent
magnets 3B are arranged in a diametrical direction of the rotor
core 2 and high-coercive-force permanent magnets 4B are arranged in
a circumferential direction on the inner circumferential side of
the rotor core 2. The other configuration is the same as that of
the sixteenth embodiment illustrated in FIG. 16A. The
permanent-magnet-type rotating electrical machine 20 employing the
rotor 1 of the embodiment is similar to that illustrated in FIG.
16B.
The high-coercive-force permanent magnets 3B and 4B each have a
magnetizing direction thickness so that a magnetized state of the
magnet can be changed with a magnetizing field created by a d-axis
current. Alternatively, the diametrically arranged
high-coercive-force permanent magnets 3B or the circumferentially
arranged high-coercive-force permanent magnets 4B have a
magnetizing direction thickness so that a magnetized state of the
magnets can be changed with a magnetizing field created by a d-axis
current.
The rotor 1 of the embodiment arranges high-coercive-force
permanent magnets as the permanent magnets 3B arranged in the
diametrical direction of the rotor core 2 and the permanent magnets
4B circumferentially arranged on the inner circumferential side of
the rotor core 2, to provide stable characteristics with respect to
disturbances such as a magnetic field generated by a load
current.
A rotating electrical machine can provide high output by cooling a
stator with water or oil and increasing a specific electric loading
(ampere-turn per unit circumferential length). This, however,
increases a magnetic field created by a load current and the strong
magnetic field created by the load current partly demagnetizes
permanent magnets. In the case of such a rotating electrical
machine of high output density, employing high-coercive-force
permanent magnets results in reducing the influence of the magnetic
field created by the load current and stabilizing the
characteristics of the permanent magnets. The permanent magnets,
however, must have a sufficient thickness so that the magnets may
be magnetized with a magnetizing field created by a d-axis current.
For example, the diametrically arranged permanent magnets 3B are
formed to be thinner than the circumferentially arranged permanent
magnets 4B, so that a small magnetizing field (small d-axis
current) is sufficient to adjust the flux amount of the permanent
magnets.
According to the embodiment, the recesses 8 are formed as needed.
The outer circumferential face of the rotor core 2 may have a true
circular section like the first embodiment illustrated in FIG. 2,
or any shape illustrated in FIGS. 7 and 9. The first hollow 5 may
have the shape illustrated in FIGS. 14 and 15. Also, the
high-coercive-force permanent magnet 3A arranged on the outer
circumferential side may have any shape illustrated in FIGS. 12,
13, and 14.
Eighteenth Embodiment
A permanent-magnet-type rotating electrical machine according to an
eighteenth embodiment of the present invention will be explained
with reference to FIG. 18. The same or equivalent parts as those of
FIGS. 2, 7 to 9, 11, and 13 to 17 are illustrated with the same
reference marks.
This embodiment is characterized in that, as illustrated in FIG.
18, a rotor core 2 is provided with slits 12 for blocking a
demagnetizing field caused by permanent magnets. On the outer
circumferential side of the rotor core 2, low-coercive-force
permanent magnets 3 are arranged in diametrical directions, and on
the inner circumferential side of the rotor core 2,
high-coercive-force permanent magnets 4 are arranged in a
circumferential direction. The slits 12 for blocking a
demagnetizing field caused by the permanent magnets are arranged in
pole portions 7 of the rotor core 2, so that the slits 12 may block
flux of the low-coercive-force permanent magnets 3 and flux of the
high-coercive-force permanent magnets 4.
The low- and high-coercive-force permanent magnets 3 and 4 are
arranged in the same iron core, and therefore, are influenced by a
demagnetizing field. For this, the embodiment interposes the slits
12 between the permanent magnets, to minimize the demagnetizing
field not to affect each permanent magnet. Accordingly, the
low-coercive-force permanent magnets 3 under load will not be
demagnetized by a demagnetizing field created by the
high-coercive-force permanent magnets 4 and a demagnetizing field
created by a load current. Also, flux of the low-coercive-force
permanent magnets 3 may easily be increased or decreased by a
magnetizing field created by a d-axis current without the influence
of the high-coercive-force permanent magnets 4. The same effect
will be obtained when the permanent magnets 3 and 4 in the rotor
core 2 are all high-coercive-force permanent magnets.
Nineteenth Embodiment
Each of the first to eighteenth embodiments mentioned above may be
configured to reverse the magnetizing direction of the
low-coercive-force permanent magnets from one to another with the
use of a magnetic field created by a current passed through a
stator coil.
A magnetizing field created by a d-axis current is used to reduce
the flux amount of permanent magnets arranged in the diametrical or
circumferential direction of the rotor 1. Reducing the flux amount
of the permanent magnets to be magnetized to zero results in
minimizing the total linkage flux amount of all permanent magnets.
The embodiment further magnetizes the permanent magnets to be
magnetized to the opposite direction, to subtract the flux thereof
from the flux of the other permanent magnets, to further reduce the
total linkage flux amount of all permanent magnets. Theoretically,
the total linkage flux amount will be zeroed. When the rotating
electrical machine is driven at high speed under no load, the
embodiment can minimize an induced voltage and iron loss.
Magnetizing directions of the permanent magnets in the second and
after the second embodiments are the same as those of the first
embodiment illustrated in FIG. 2.
* * * * *